Technical Abstract:
Enhancing the nutritional quality of crops is of international importance, and multiple methods have been utilized to increase the nutrient content of legume seeds. Because nutrients mobilized from source leaves to growing reproductive sink tissues greatly contribute to the final composition of the mature seeds, manipulating the mobilization of minerals stored in source tissues is one potential strategy for increasing final seed mineral concentration. It has previously been reported that seeds of the model legume Medicago truncatula ecotype A17 contain a lower Fe concentration compared to ecotype DZA315.16. We hypothesized that this difference was due, in part, to variation in source leaf processes and sought to expose these distinctions by challenging both ecotypes with long-term Fe-deficiency. As expected, when challenged with Fe deficiency for 30 days, growth of both A17 and DZA315.16 plants significantly decreased relative to controls. Interestingly, Fe-deficient A17 plants also displayed an increase in the relative proportion of live leaf tissue with respect to the total mass, while similarly treated DZA315.16 plants did not. Instead, the proportion of abscised leaves in DZA315.16 increased with long-term Fe-deficiency. Moreover, the mass of abscised pods tended to be higher in A17 than DZA315.16. Taken together, these data suggest that, under stress, nutrients in A17 source leaves are reserved to sustain the metabolic activities of leaves rather than being mobilized to support pod growth.